Missing definition for unsigned extrinsics

[josepot]

The spec briefly mentions the fact that a transaction can be unsigned:

The most significant bit of Tv indicates whether the transaction is signed (1) or unsigned (0). The remaining 7-bits represent the version number. As an example, for extrinsic format version 4, a signed extrinsic represents Tv as 132 while an unsigned extrinsic represents it as 4.

However, in the definition of extrinsic version 4, it assumes that the extrinsic is signed and there is no mention whatsoever about the fields or the shape of an unsigned extrinsic. Therefore, the formal definition for v4 is incorrect (or incomplete) because it doesn't account for unsigned extrinsics.